This invention relates to a device for removing condensate from steam lines, and more particularly, relates to valves for purging particulate or other debris from the pipe lines or conduits through which live steam is conducted.
In steam piping systems, the condensate which accumulates is drained from the steam lines and generally returned to the steam boiler through condensate-return lines. The condensate-return lines usually include a debris strainer device which filters particulate debris, such as calcium carbonate, copper and oxides of copper particles, from the mixture of steam and condensate which flows through the strainer device into a so-called "steam trap" device. Typically, steam-traps, such as the familiar inverted, bucket traps, have been replaced with so-called orifice devices, typified in U.S. Pat. No. 4,426,213; in such orifice devices, the condensate obstructs the passage of steam through the orifice in order to minimize steam loss while permitting drainage of the condensate.
The conventional strainer device includes a filter screen which filters out the larger particulates from the condensate and steam mixture but permits passage of the mixture with smaller particulates. The particulates must be removed periodically in order to prevent plugging of the strainer device. To facilitate removal of the filtered particulates in an operation referred to as steam "blow-off", the strainer device is provided with an opening or port through which the blow-off is expelled. The blow-off opening normally is closed by either a simple, removable plug, such as described in U.S. Pat. No. 4,171,209, or with a blow-off valve which provides greater convenience in the blow-off operation. Usually, blow-off is performed when the strainer device is under full steam pressure so that the pressurized steam and condensate mixture dislodges the accumulated particles from the strainer and screen during the discharge.
The typical blow-off valve is a quick-acting device, for example, a ball valve, gate valve, or glove valve, through which the sudden, blow-off discharge creates a danger of burning the operator who opens the blow-off valve. Another disadvantage of the conventional blow-off valve is its susceptibility to rupturing due to freezing of unduly large columns of collected condensate in the strainer housing or valve housing. In many outdoor installations, a periodic shut down of steam operation in cold weather will permit the accumulation of such unduly large amounts of condensate in the strainer and valve to freeze when effort has not been made to manually drain the blow-off valve.
When the strainer is provided with a simple, removable plug, the danger of such a burn requires that the strainer be isolated from the steam system by closing valves both upstream and downstream in order to allow the strainer to cool down, thereby allowing the trapped steam to condense before it is safe to remove the plug. Thus, only after the plug is removed, can the upstream valve be opened to allow the blow-off discharge; and the upstream valve must once again be closed to allow reinstallation of the plug. Subsequent, normal operation requires the shut-off valves to be opened again. This cumbersome procedure has resulted in the alternative provision of blow-off valves in many strainer installations with the consequent danger of sudden blow-off discharge.